Many varieties of two-way radio communications systems are known in the art. FIG. 1 is a block diagram illustrating both a typical conventional radio system 101 and a trunked radio system 103. In the conventional radio system 101, a plurality of subscriber units are formed into talkgroups. Each talkgroup is permanently assigned to a separate channel for communication. Thus, each talkgroup is served by one channel. In contrast, the trunked radio system 103 and its subscriber units use a pool of channels for virtually an unlimited number of talkgroups. Thus, all talkgroups are served by all channels. The trunked radio system 103 works to take advantage of the probability that not all talkgroups need a channel for communication at the same time. Estimates are made about how much load a typical user presents to the system in terms of calls per hour and duration of each call. For a traffic load, fewer channels are required since all talkgroups are served by all channels. Combining this with the number of users on the system, and the acceptable quality of service (QoS), determines how many trunked channels are required to satisfactorily serve the number of users. With a given number of channels, a much greater number of talkgroups can be accommodated as compared with conventional radio systems. Hence, a primary purpose of a trunked radio system is the efficient utilization of channels allowing for more users to carry many conversations over a fewer number of distinct channels.
As seen in FIG. 2, a conventional trunked radio system 201 uses a dedicated or exclusive channel, which is often referred to as a control channel 205, for handling call requests and for assigning particular traffic channels (CH's 1-3) to particular groups of subscriber units for a call. An infrastructure controller 207 controls what is broadcast on the control channel 205 via a control channel repeater. Other terms that sometimes refer to the infrastructure controller 207 include trunking controller, site controller, resource allocator, channel allocator, controller, and other like terms. The infrastructure controller 207 continuously, periodically, or intermittently causes the control channel repeater to broadcast a control signal on the control channel 205, so that subscriber units can locate the control channel 205, transmit new call requests on the control channel 205, and monitor the control channel 205 for new call requests that they may be interested in joining.
In order to start a group call (i.e., a one-to-many call), a subscriber unit requests, via a transmission on the control channel 205 to the infrastructure controller 207, that a traffic channel is allocated for its use, and the infrastructure controller 207 transmits instructions back, on the control channel 205, telling subscriber units in the group that are interested in the call to switch to the traffic channel assigned for that call. A similar process may be followed when a subscriber unit starts an individual call (i.e., a one-to-one call). In the example set forth in FIG. 2, subscriber units 1 and 2, after one of them had transmitted a request on the control channel 205, have been assigned traffic channel CH 1 to transmit call traffic on, and subscriber units 3, 4, 5, and 6, after one of them had transmitted a request on the control channel 205, have been assigned traffic channel CH 3 to transmit call traffic on.
In other types of trunked systems, the control channel 205 may be switched to a traffic channel for a newly requested call, and all subscriber units not interested in the new call instructed to move to a new channel that will become the new control channel for the remaining subscriber units.
One disadvantage of the trunked radio system 201 is that an infrastructure controller 207 and a control channel repeater is required to maintain control over channel assignments and the control channel repeater is required to continually, periodically, or intermittently broadcast a control signal on the control channel 205 so that subscriber units can find the control channel 205 and so that centralized control over traffic channel assignments may be provided.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.